Re: [testsuite & dwarf2] How to handle store.exp failure on AMD64?

[Andrew Cagney <ac131313@redhat.com>]

Ref: Dwarf unwinder problems with store.exp and preserved regs
http://sources.redhat.com/ml/gdb/2003-07/msg00026.html

> Andrew Cagney wrote:
> For this specific ABI and problem, did GCC put the value in a preserved regiter ...
> 
> - GCC -O0 should should not eliminate variables, and should preserve all variables across function calls.
> 
> Given that is compiled with -O0, I think GCC is failing on count #3 here.
> 
> or a scratch register?
> 
> Into the preserved register (%rbx).
> When I added the appropriate DW_CFA_same_value instruction to the .s file, the register was correctly unwound and the value of the variable in an upper frame shown.

Ok.  Looking at the debug info (bet everyones compiler is different :-/) 
I'm seeing a very non-descrptive CIEs vis:

00000018 00000014 ffffffff CIE
   Version:               1
   Augmentation:          ""
   Code alignment factor: 1
   Data alignment factor: -8
   Return address column: 16

   DW_CFA_def_cfa: r7 ofs 8
   DW_CFA_offset: r16 at cfa-8
   DW_CFA_nop
   DW_CFA_nop
   DW_CFA_nop
   DW_CFA_nop
   DW_CFA_nop
   DW_CFA_nop

I would have expected the CIE.INITIAL_INSTRUCTIONS to specify the 
default state of all DWARF2 registers, and not just a select few.  The 
dwarf2 example, spells out the initial state of all registers vis:

cie              32                             length
cie+4            0xffffffff                     CIE_id
cie+8            1                              version
cie+9            0                              augmentation
cie+10           4                              code_alignment_fact
cie+11           -4                             data_alignment_fact
cie+12           8                              R8 is the return ad
cie+13           DW_CFA_def_cfa (7, 0)          CFA = [R7]+0
cie+16           DW_CFA_same_value (0)          R0 not modified (=0
cie+18           DW_CFA_undefined (1)           R1 scratch
cie+20           DW_CFA_undefined (2)           R2 scratch
cie+22           DW_CFA_undefined (3)           R3 scratch
cie+24           DW_CFA_same_value (4)          R4 preserve
cie+26           DW_CFA_same_value (5)          R5 preserve
cie+28           DW_CFA_same_value (6)          R6 preserve
cie+30           DW_CFA_same_value (7)          R7 preserve
cie+32           DW_CFA_register (8, 1)         R8 is in R1
cie+35           DW_CFA_nop                     padding
cie+36

and GCC put simply is not doing this.

Andrew